Fuel cell separator and its manufacturing method

ABSTRACT

Fuel cell separators ( 18 ) sandwich an anode ( 13 ) and a cathode ( 14 ) which are installed along both sides of an electrolyte film ( 12 ) and diffusion layers ( 16, 16 ). The separators ( 18 ) are made of a mixture material containing a thermoplastic resin selected from ethylene-vinyl acetate copolymers and ethylene-ethyl acrylate copolymers and carbon particles selected from at least one of Ketjen black, graphite and acetylene black. Since the thermoplastic resin is excellent in especially flexibility, the contact surfaces of the separators ( 18 ) in contact with the diffusion layers ( 15, 16 ) can be a portion excellent in sealability by adding the thermo-plastic resin excellent in sealability to the separators ( 18 ).

TECHNICAL FIELD

This invention relates to a fuel cell separator and a manufacturingmethod thereof, and particularly to a fuel cell separator forconstituting a cell module by sandwiching from both sides an anode and acathode set against an electrolyte film, and a manufacturing methodthereof.

BACKGROUND ART

A fuel cell is a cell which utilizes the opposite principle to theelectrolysis of water to obtain electricity by the process of reactinghydrogen with oxygen to obtain water. Because generally a fuel gas issubstituted for hydrogen and air or an oxidant gas is substituted foroxygen, the terms fuel gas, air and oxidant gas are often used. In thefollowing, the basic construction of an ordinary fuel cell will bedescribed with reference to FIG. 15.

As shown in FIG. 15, a cell module of a fuel cell 200 is made bydisposing an anode 202 and a cathode 203 on opposite faces of anelectrolyte film 201 and sandwiching these electrodes 202, 203 with afirst separator 206 and a second separator 207 via diffusion layers 204,205. A fuel cell 200 is obtained by stacking many of these cell modulestogether.

It is necessary for the fuel gas to be brought into contact with theanode 202 effectively. To this end, many grooves (not shown) areprovided in the face 206 a of the first separator 206, and by thegrooves being covered when the diffusion layer 204 is disposed on theface 206 a of the first separator 206, first flow passages (not shown)constituting fuel gas flow passages are formed.

It is necessary for the oxidant gas to be brought into contact with thecathode 203 effectively. To this end, many grooves 208 . . . areprovided in the face 207 a of the second separator 207, and by thegrooves 208 . . . being covered when the diffusion layer 205 is disposedon the face 207 a of the second separator 207, second flow passages (notshown) constituting oxidant gas flow passages are formed.

And in the first separator 206, many cooling water passage grooves 209 .. . are provided in the reverse face 206 b to the face 206 a, and manycooling water passage grooves (not shown) are provided in the reverseface 207 b to the face 207 a in the second separator 207. By the firstand second separators 206, 207 being brought face to face, the coolingwater passage grooves 209 . . . of each are brought together to formcooling water passages (not shown).

As a method of manufacturing these first and second separators 206 and207, for example the ‘Fuel Cell Separator and Manufacturing MethodThereof’ in Japanese Patent Publication JP-A-2001-126744 is known.

In this published manufacturing method, conductive particles mixed witha thermoplastic resin are heated and kneaded; this mixture isextrusion-molded and formed into a long sheet with rollers; this longsheet is cut to predetermined dimensions to make blanks; and first andsecond separators 206, 207 are obtained by forming gas passage andcooling water passage grooves in both sides or one side of these blanks.

To form the first and second flow passages by bringing the diffusionlayers 204, 205 together with the first and second separators 206, 207,it is necessary for the diffusion layers 204, 205 to be brought togetherwith the respective faces 206 a, 207 a of the first and secondseparators 206, 207 in an intimately contacting state. However, to bringthe diffusion layers 204, 205 together with the faces 206 a, 207 a ofthe first and second separators 206, 207 in an intimately contactingstate is difficult, and there is a risk of gaps arising locally betweenthe faces 206 a, 207 a of the first and second separators and thediffusion layers 204, 205.

Because the cooling water passages are formed in the first separator 206and the second separator 207 by these two being brought together, it isnecessary for the first separator 206 and the second separator 207 to bebrought together in an intimately contacting state. However, to bringthe first separator 206 and the second separator 207 together in anintimately contacting state is difficult, and there is a risk of gapsarising locally between the first separator 206 and the second separator207.

Because of this, the development of a fuel cell separator has beenawaited with which it is possible to bring together the faces 206 a, 207a of the first and second separators 206, 207 with the diffusion layers204, 205 in an intimately contacting state and also it is possible tobring together the first separator 206 and the second separator 207 inan intimately contacting state.

In a fuel cell separator manufacturing method of related art, a longsheet is cut to predetermined dimensions to make blanks and then groovesfor gas passages and cooling water passages are formed after that in theindividual blanks. With this fuel cell separator manufacturing method,when the grooves are formed in the blanks, each individual blank has tobe positioned in a correct position. Consequently, the positioning ofthe blanks takes time, and this has been a hindrance to raisingproductivity. Because of this, the development of a manufacturing methodhas been awaited with which it is possible to mold fuel cell separatorsefficiently.

Known fuel cells include those which, as shown in for example JapanesePatent Publication JP-A-2002-97375, ‘Thermoplastic Resin Composition andMolding’, carbon fibers or carbon nanotubes are blended withthermoplastic resin as a fuel cell separator composition. The content ofthis publication will now be discussed in detail.

When a separator is assembled to a fuel cell, it is necessary for manygas passage grooves and cooling water passage grooves to be molded inboth sides of it. Consequently, a starting material having excellentmoldability must be used for the separator. Also, a function ofcollecting current from an electrode is required of the separator, andso it must have excellent electrical conductivity. To fulfil theserequirements, in this known technology, as the constituents of theseparator, polyphenylene sulfide (a thermoplastic resin), which hasexcellent moldability, is used, and carbon fibers or carbon nanotubes,which have excellent electrical conductivity, are used.

Explaining an example in detail, as constituents of a separator, 30 wt %of carbon fibers, 0.5 wt % of carbon nanotubes, and 69.5 wt % ofpolyphenylene sulfide (thermoplastic resin) were prepared, and thesewere mixed to obtain a mixture. Thereafter, separators wereinjection-molded with this mixture as the starting material.

By using 69.5 wt % of the thermoplastic resin polyphenylene sulfide,good injection-moldability can be secured. And by using 30 wt % ofcarbon fiber and 0.5 wt % of carbon nanotubes, a certain level ofelectrical conductivity is secured.

However, in the publication mentioned above, because a large amount ofcarbon fiber is included in the starting material, directionality of thecarbon fiber occurs markedly, and the separator becomes anisotropic.Consequently, there is a risk of warping and distortion arising in theseparator.

When there are gas passage grooves and cooling water passage grooves inboth sides as in a separator, weld lines tend to appear. Consequently,there is a risk of the strength of the separator falling drastically.

Also, in the above-mentioned publication, to raise the electricalconductivity of the separator, carbon fibers and carbon nanotubes areincluded in the separator starting material. However, it is difficult toraise the electrical conductivity sufficiently by including carbonfibers in the starting material.

Specifically, in the above-mentioned publication, the volume resistivityis measured by the double ring method (ASTM D257). However, the doublering method is suited for the measure-ment of high resistances, and inmeasurement results obtained by the present inventors it was found thatcompared to four probe method, which is suited to the measurement of lowresistances, volume resistivities are considerably lower.

Furthermore, in the last few years high performance has come to berequired of fuel cells, and to satisfy this requirement the introductionof separators having still better conductivity is awaited.

DISCLOSURE OF THE INVENTION

In a first aspect, this invention provides a fuel cell separator forsandwiching from both sides via diffusion layers an anode and a cathodeset against an electrolyte film, made of a mixture of a thermoplasticresin selected from among ethylene/vinyl acetate copolymers andethylene/ethyl acrylate copolymers and a at least one type of carbonparticle selected from Ketjen black, graphite and acetylene black.

Ethylene/vinyl acetate copolymers and ethylene/ethyl acrylate copolymershave particularly good flexibility even among thermoplastic resins. Byincluding a thermoplastic resin with superior flexibility like this inthe separator, the contact faces of the separator that make contact withthe diffusion layers are given elasticity, and the contact faces aregiven an excellent sealing characteristic. Consequently, the matingparts of the separator contact faces and the diffusion layers can bekept intimate. Therefore, it is not necessary for a seal material to beapplied between the separator contact faces and the diffusion layers.

And, as a result of just including a thermoplastic resin selected fromamong ethylene/vinyl acetate copolymers and ethylene/ethyl acrylatecopolymers in the separator, the separator contact faces are changedinto parts having a good sealing characteristic. By this means it ispossible to produce a well-sealing separator with good efficiency.

On the other hand, the carbon particles consisting of Ketjen black,graphite and/or acetylene black have electrical conductivity, and bythese carbon particles being included in the separator, conductivity ofthe separator is secured.

Preferably, the proportion of the thermoplastic resin in the mixture ismade 14 to 20 wt % and the proportion of the carbon particles is 80 to86 wt %.

The reasons for setting the proportion of the thermoplastic resin to 14to 20 wt % are as follows. That is, when the thermoplastic resin contentis less than 14 wt %, it is difficult to secure enough elasticity, i.e.sealing characteristic, of the contact faces of the separator, becausethe thermoplastic resin content is too low. When on the other hand thethermoplastic resin content exceeds 20 wt %, the amount of the carbonparticle included in the separator is too low, and it is difficult tosecure conductivity of the separator adequately. Accordingly, thethermoplastic resin content was set to 14 to 20 wt % to secure sealingcharacteristic of the separator and adequately secure electricalconductivity of the separator.

Preferably, 3 to 20 wt % of the carbon particles is made Ketjen black.

Ketjen black is a material with particularly good electricalconductivity compared to other carbon blacks, and by Ketjen black beingincluded the electrical conductivity of the separator is raised. Thereasons for setting the Ketjen black content to 3 to 20 wt % are that ifthe Ketjen black content is less than 3 wt % then it is difficult toobtain an effect of having included Ketjen black because the Ketjenblack content is too low. Consequently, when the Ketjen black content isless than 3 wt %, there is a risk of it not being possible to secureelectrical conductivity of the separator adequately.

If on the other hand the Ketjen black content exceeds 20 wt %, kneadingbecomes difficult because the Ketjen black content is too large.Although it is conceivable to make kneading possible by adding asolvent, there is a risk of costs increasing as a result of using asolvent. Furthermore, even if a solvent is added and kneading iscompleted successfully, the fluidity of the knead including the Ketjenblack is poor and for example at the time of molding it is difficult toobtain the predetermined shape.

Accordingly, the Ketjen black content was set to 3 to 20 wt % to secureadequate electrical conductivity of the separator and also achievefacilitation of kneading and secure moldability well.

Preferably, the proportions in the mixture are made 14 to 20 wt %thermoplastic resin, 70 to 83.5 wt % carbon particle, and 2.5 to 10 wt %glass fiber or carbon fiber.

By glass fiber or carbon fiber being mixed into the mixture, therigidity of the separator is raised. The reasons for setting the glassfiber or carbon fiber content to 2.5 to 10 wt % are that when the glassfiber or carbon fiber content is less than 2.5 wt %, it is difficult toraise the rigidity of the separator because the glass fiber or carbonfiber content is too low. When on the other hand the glass fiber orcarbon fiber content exceeds 10 wt %, the glass fiber or carbon fibercontent is too large and it is difficult to disperse the glass fiber orcarbon fiber uniformly in the mixture and extrusion-molding and pressingof the mixture become problematic. Accordingly, the glass fiber orcarbon fiber content was set to 2.5 to 10 wt %, to ensure a sufficientglass fiber or carbon fiber content and raise the rigidity of theseparator, and to disperse the glass fiber or carbon fiber uniformly andobtain a mixture with good moldability and thereby raise productivity.

In a second aspect, the invention provides a method for manufacturing afuel cell separator, including: a step of selecting a thermoplasticresin from among ethylene/vinyl acetate copolymers and ethylene/ethylacrylate copolymers and selecting at least one type of carbon particlesfrom Ketjen black, graphite and acetylene black; a step of obtaining amixture by mixing the selected thermoplastic resin and carbon particles;a step of obtaining a sheet material by extrusion-molding the mixturewith an extruder; a step of forming gas flow passage grooves in thesurface of the sheet material by pressing it; and a step of obtainingfuel cell separators by cutting the sheet material with the gas flowpassages formed in it to a predetermined shape.

With the mixture in the form of a sheet material, gas passage groovesare press-formed in its surface and then the sheet material is cut to apredetermined shape to obtain separators. By press-forming the gaspassage grooves into the material in sheet form in this way it ispossible to form the gas passage grooves continuously with goodefficiency and to raise the productivity of the separator.

In a third aspect, the invention provides a fuel cell separator forsandwiching from both sides via diffusion layers an anode and a cathodeset against an electrolyte film, characterized in that it is made of amixture including 10 to 34 wt % polyphenylene sulfide, 65 to 80 wt %graphite, and 1 to 10 wt % Ketjen black.

In this case, 10 to 34 wt % of polyphenylene sulfide, serving as athermoplastic resin, is included in the separator. Because polyphenylenesulfide has excellent moldability and excellent flexibility, it raisesthe moldability when the separator is injection-molded, and a separatorhaving a good sealing characteristic is obtained. By this means it ispossible to raise further the productivity and accuracy of theseparator. Also, because polyphenylene sulfide is a resin that has goodheat-resistance, including the polyphenylene sulfide in the separatorraises the heat-resistance of the separator. Consequently, it becomespossible to apply the separator to fuel cells used at relatively hightemperatures, and the range of applications can be enlarged.

The reasons for setting the polyphenylene sulfide content to 10 to 34 wt% are as follows. That is, when the polyphenylene sulfide content isless than 10 wt %, the polyphenylene sulfide content is too low and itbecomes difficult to secure moldability of the separator and elasticityof the separator, i.e. sealing characteristic. Also, when the content isless than 10 wt %, it is difficult to secure heat-resistance of theseparator and to make it work as a bonding agent. When on the other handthe polyphenylene sulfide content exceeds 34 wt %, the graphite contentin the separator is too small and it is difficult to secure adequateelectrical conductivity of the separator. Accordingly, the polyphenylenesulfide content was set to 10 to 34 wt % to secure moldability, sealingcharacteristic and heat-resistance of the separator and to secure asufficient electrical conductivity.

Also, by including 65 to 80 wt % of graphite in the separator, itselectrical conductivity was raised.

The reasons for setting the graphite content to 65 to 80 wt % are asfollows. That is, when the graphite content is less than 65 wt %, it isdifficult to raise the electrical conductivity of the separator becausethe graphite content is too small. When on the other hand the graphitecontent exceeds 80 wt %, the graphite content is too large and itbecomes difficult to disperse the graphite uniformly and theextrusion-molding and press-forming become problematic. Accordingly, thegraphite content was set to 65 to 80 wt %, to secure electricalconductivity of the separator and to secure moldability. And, by makingthe graphite content over 65 wt %, it is possible to reduce the volumeresistivity of the separator and raise the electrical conductivity ofthe separator amply. Furthermore, by including 1 to 10 wt % of Ketjenblack, it is possible to raise the electrical conductivity stillfurther.

Ketjen black is a material having particularly good conductivitycompared to other carbon blacks, and by including Ketjen black in theseparator it is possible to make the electrical conductivity of theseparator higher.

The reasons for setting the Ketjen black content to 1 to 10 wt % are asfollows. That is, when the Ketjen black content is less than 1 wt %, theKetjen black content is too low, and there is a risk of not beingpossible to secure conductivity of the separator adequately. On theother hand, when the Ketjen black content exceeds 10 wt %, kneadingbecomes difficult because the Ketjen black content is too large.Although it is conceivable to make kneading possible by adding asolvent, there is a risk of costs increasing as a result of using asolvent. Furthermore, even if a solvent is added for kneading, thefluidity of the knead including the Ketjen black is relatively poor andfor example at the time of molding it is difficult to obtain thepredetermined shape. Accordingly, the Ketjen black content was made 1 to10 wt %, and the electrical conductivity was thereby raised stillfurther.

The graphite and Ketjen black included in the separator are carbonparticles, and no large quantity of fibrous material is included in theseparator. Therefore, the occurrence of directionality in the separatorcaused by fibrous material is suppressed, and warping and distortionarising in the separator as a result of anisotropy is prevented. Also,because no large quantity of fibrous material is included in theseparator, the strength of the separator is prevented from falling dueto weld lines arising in the gas passage grooves and the cooling waterpassage grooves provided on the separator.

In a preferable form of the invention, the above-mentioned mixtureincludes 5 to 15 wt % of chopped carbon fiber, and the graphite includedin this mixture is made 60 to 80 wt %.

By 5 to 15 wt % of chopped carbon fiber being included in the separator,the strength and the heat-resistance of the separator are raised. Whenchopped carbon fiber is included, because this performs some of thefunction of the graphite, the lower limit value of the graphite contentcan be 60 wt %.

The reasons for setting the chopped carbon fiber content to 5 to 15 wt %are as follows. That is, when the chopped carbon fiber content is lessthan 5 wt %, the chopped carbon fiber content is too small and it isdifficult to secure strength and heat-resistance of the separator. Onthe other hand, when the chopped carbon fiber content exceeds 15 wt %,the amount of the chopped carbon fiber included in the separator is toolarge and the directionality of the chopped carbon fiber manifestsconspicuously and the separator becomes anisotropic. Consequently, thereis a risk of warping and distortion arising in the separator. And, whenas in a separator there are gas passage grooves and cooling waterpassage grooves in the side faces, weld lines tend to appear.Consequently, there is a risk of the strength of the separator fallingdrastically. Accordingly, the chopped carbon fiber content was set to 5to 15 wt %.

Preferably, the viscosity of the polyphenylene sulfide is 20 to 80 psi.

By making the viscosity of the polyphenylene sulfide 20 to 80 psi, it ispossible to knead the graphite into the polyphenylene sulfide well andraise the moldability of the separator further.

The reasons for setting the viscosity of the polyphenylene sulfide to 20to 80 psi are as follows. That is, when the viscosity of thepolyphenylene sulfide is less than 20 psi, the viscosity is too low andthe polyphenylene sulfide does not harden and forms a slurry. On theother hand, when the viscosity of the polyphenylene sulfide exceeds 80psi, the viscosity of the polyphenylene sulfide is too high and thegraphite and so on cannot be kneaded well into the polyphenylenesulfide. Accordingly, the viscosity of the polyphenylene sulfide was setto 20 to 80 psi, whereby it is made possible to knead the graphite andso on into the polyphenylene sulfide well and the moldability of theseparator is raised further.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing a fuel cell with fuelcell separators according to a first embodiment of the invention;

FIG. 2 is a sectional view on the line A-A in FIG. 1;

FIG. 3 is a sectional view on the line B-B in FIG. 1;

FIG. 4 is a sectional view of a fuel cell separator shown in FIG. 1;

FIG. 5 is a flow chart of a method for manufacturing a fuel cellseparator according to the first embodiment of the invention;

FIG. 6A and FIG. 6B are views illustrating a step of forming a mixtureinto pellets in the manufacturing method;

FIG. 7 is a view illustrating a pressing step in the manufacturingmethod;

FIG. 8 is an exploded perspective view showing a fuel cell with fuelcell separators according to a second embodiment of the invention;

FIG. 9 is a sectional view on the line C-C in FIG. 8;

FIG. 10 is a sectional view on the line D-D in FIG. 8;

FIG. 11 is a sectional view of a fuel cell separator shown in FIG. 8;

FIG. 12 is a view illustrating a method of obtaining a volumeresistivity;

FIG. 13 is a graph showing a relationship between graphite content andvolume resistivity;

FIG. 14 is a graph showing a relationship between Ketjen black contentand volume resistivity; and

FIG. 15 is an exploded perspective view showing a fuel cell of relatedart.

BEST MODES FOR CARRYING OUT THE INVENTION

As shown in FIG. 1, a fuel cell 10 is a solid polymer type fuel cellmade by constructing cell modules 11 by using for example a solidpolymer electrolyte as an electrolyte film 12, appending an anode 13 anda cathode 14 to this electrolyte film 12, disposing a separator 18 onthe anode 13 side via an anode diffusion layer 15 and disposing aseparator (fuel cell separator) 18 on the cathode 14 via a cathodediffusion layer 16, and stacking many of these cell modules 11 together.

The separator 18 is made up of a first separator 20 and a secondseparator 30, and has a cooling water passage formation face 20 a of thefirst separator 20 and a bonding face 30 a of the second separator 30bonded together by for example vibration welding.

By the first and second separators 20, 30 being vibration-weldedtogether like this, cooling water passage grooves 21 . . . in the firstseparator 20 are covered by the second separator 30 and form coolingwater passages 22 . . . (see FIG. 4).

Cooling water supply openings 23 a, 33 a in the centers of the top endsof the first and second separators 20, 30 and cooling water dischargeopenings 23 b, 33 b in the centers of the bottom ends of the first andsecond separators 20, 30 connect with these cooling water passages 22 .. . .

The first separator 20 has fuel gas passage grooves 24 . . . (see FIG.2) on a fuel gas passage formation face (contact face) 20 b, and by theanode diffusion layer 15 being placed on the fuel gas passage formationface 20 b the anode diffusion layer 15 covers the fuel gas passagegrooves 24 . . . and forms fuel gas passages 25 . . . (see FIG. 4).

Fuel gas supply openings 26 a, 36 a in the left sides of the top ends ofthe first and second separators 20, 30 and fuel gas discharge openings26 b, 36 b in the right sides of the bottom ends of the first and secondseparators 20, 30 are connected to these fuel gas passages 25 . . . .

The second separator 30 has oxidant gas passage grooves 37 . . . in anoxidant gas passage formation face (contact face) 30 b, and by thecathode diffusion layer 16 being placed on the oxidant gas passageformation face 30 b the cathode diffusion layer 16 covers the oxidantgas passage grooves 37 . . . and forms oxidant gas passages 38 . . .(see FIG. 4).

Oxidant gas supply openings 29 a, 39 a in the right sides of the topends of the first and second separators 20, 30 and oxidant gas dischargeopenings 29 b, 39 b in the left sides of the bottom ends of the firstand second separators 20, 30 are connected to the oxidant gas passages38 . . . .

As the resin for making the first and second separators 20, 30, amixture made by mixing a thermoplastic resin selected from amongethylene/vinyl acetate copolymers and ethylene/ethyl acrylatecopolymers, carbon particles (a carbon material) selected from at leastone among Ketjen black, graphite and acetylene black, and glass fibersor carbon fibers is used.

In this mixture, the proportion of the thermoplastic resin is 14 to 20wt %; the proportion of the carbon particles is 80 to 86 wt %; and the80 to 86 wt % of carbon particles include 3 to 20 wt % of Ketjen black.

Ketjen black is a carbon black having excellent electrical conductivity,and for example one made by Ketjen Black International Co., Ltd. (soldby Mitsubishi Chemical Co., Ltd.) is suitable, although the invention isnot limited to this.

Ethylene/ethyl acrylate copolymers and ethylene/ethyl acrylatecopolymers are resins having flexibility among thermoplastic resins, andby these resins being used the first and second separators 20, 30 aremade very flexible members.

Ketjen black, graphite and acetylene black are materials havingexcellent electrical conductivity, and by carbon particles selected fromat least one among Ketjen black, graphite and acetylene black being usedthe first and second separators 20, 30 are made members having excellentelectrical conductivity.

The reasons for setting the proportion of the thermoplastic resin to 14to 20 wt % are as follows.

When the thermoplastic resin content is less than 14 wt %, thethermoplastic resin content is too small and it is difficult to secureflexibility, i.e. elasticity, of the contact faces of the first andsecond separators 20, 30.

On the other hand, when the thermoplastic resin content exceeds 20 wt %,the thermoplastic resin content is too large and it is difficult tomaintain the required volume resistivity (Ω·cm), and it becomesproblematic to secure adequate electrical conductivity of the first andsecond separators 20, 30.

Accordingly, the thermoplastic resin content is set to 14 to 20 wt %,whereby elasticity of the first and second separators 20, 30 is securedand a sufficient electrical conductivity is secured.

The reasons for setting the carbon particle content to 80 to 86 wt % areas follows.

When the carbon particle content exceeds 86 wt %, the carbon particlecontent is too large and it is difficult to disperse the carbonparticles uniformly, and extrusion-molding and press-forming becomeproblematic. Therefore, the carbon particle content should be set to 86wt % or lower.

And by the carbon particle content being kept 70 wt % and above, thevolume resistivity (Ω·cm) of the first and second separators 20, 30 isreduced and the electrical conductivity of the first and secondseparators 20, 30 is sufficiently raised. Because of this, the carbonparticle content should be kept to 70 wt % or greater.

However, because 14 to 20 wt % of the thermoplastic resin is included inthe first and second separators 20, 30, in the first embodiment, thecarbon particle content is made 80 wt % or more, to secure an ampleelectrical conductivity of the first and second separators 20, 30.

Ketjen black is a carbon particle with superior electrical conductivitycompared to ordinary carbon black. Because of this, by Ketjen blackbeing used, the volume resistivity (Ω·cm) of the first and secondseparators 20, 30 is greatly reduced. The included amount of this Ketjenblack is set to 3 to 20 wt %.

The reasons for setting the Ketjen black content to 3 to 20 wt % are asfollows.

When the Ketjen black content is less than 3 wt %, the Ketjen blackcontent is too small and it is difficult to obtain an effect of havingincluded Ketjen black. Consequently, when the Ketjen black content isless than 3 wt %, there is a risk of not being possible to secureelectrical conductivity of the separator adequately.

If on the other hand the Ketjen black content exceeds 20 wt %, kneadingbecomes difficult because the Ketjen black content is too large.Although it is conceivable to make kneading possible by adding asolvent, there is a risk of costs increasing as a result of using asolvent.

Furthermore, even if a solvent is added and kneading is completedsuccessfully, the fluidity of the knead including the Ketjen black ispoor and for example at the time of molding it is difficult to obtainthe predetermined shape.

Accordingly, the Ketjen black content was set to 3 to 20 wt %, wherebyadequate electrical conductivity of the separator is secured and alsofacilitation of kneading is achieved and good moldability is secured.

Next, referring to FIG. 2, the first separator 20 is a member formed ina substantially rectangular shape (see FIG. 1), and has many coolingwater passage grooves 21 . . . in a cooling water passage formation face20 a and has many fuel gas passage grooves 24 . . . in a fuel gaspassage formation face (contact face) 20 b.

A thermoplastic resin selected from among ethylene/vinyl acetatecopolymers and ethylene/ethyl acrylate copolymers is included in thefirst separator 20. Ethylene/vinyl acetate copolymers and ethylene/ethylacrylate copolymers are thermoplastic resins having particularly goodflexibility.

Therefore, by either of these very flexible thermoplastic resins beingincluded in the first separator 20, the fuel gas passage formation face20 b is given elasticity.

Also, as a result of just including a thermoplastic resin selected fromamong ethylene/vinyl acetate copolymers and ethylene/ethyl acrylatecopolymers in the first separator 20, the fuel gas passage formationface 20 b is changed into a part having a good sealing characteristic.By this means it is possible to produce a well-sealing first separator20 with good efficiency.

As shown in FIG. 3, the second separator 30 is a member formed in asubstantially rectangular shape as shown in FIG. 1, and has a bondingface 30 a formed flat and has many oxidant gas passage grooves 37 . . .in an oxidant gas passage formation face (contact face) 30 b.

A thermoplastic resin selected from among ethylene/vinyl acetatecopolymers and ethylene/ethyl acrylate copolymers is included in thesecond separator 30. Ethylene/vinyl acetate copolymers andethylene/ethyl acrylate copolymers are thermoplastic resins havingparticularly good flexibility.

Therefore, by either of these very flexible thermoplastic resins beingincluded in the second separator 30, the oxidant gas passage formationface 30 b is given elasticity.

Also, as a result of just including a thermoplastic resin selected fromamong ethylene/vinyl acetate copolymers and ethylene/ethyl acrylatecopolymers in the second separator 30, the oxidant gas passage formationface 30 b is changed into a part having a good sealing characteristic.By this means it is possible to produce a well-sealing second separator30 with good efficiency.

Reference will now be made to FIG. 4, which shows the electrodediffusion layers 15, 16 stacked with the separator 18.

The separator 18 is made by bringing together the first and secondseparators 20, 30 and then applying a welding pressure to the first andsecond separators 20, 30 and vibrating one or the other of the first andsecond separators 20, 30 to produce frictional heat, therebyvibration-welding the cooling water passage formation face 20 a of thefirst separator 20 and the bonding face 30 a of the second separator 30together and covering the cooling water passage grooves 21 of the firstseparator 20 with the second separator 30 and forming cooling waterpassages 22.

By the anode diffusion layer 15 being brought together with the fuel gaspassage formation face 20 b, fuel gas passages 25 . . . are formed bythe fuel gas passage grooves 24 . . . and the anode diffusion layer 15.

Here, by including a thermoplastic resin having good flexibility in thefirst separator 20 it is possible to give the fuel gas passage formationface 20 b elasticity and make the fuel gas passage formation face 20 b apart having a good sealing characteristic.

Consequently, the mating parts of the fuel gas passage formation face 20b and the anode diffusion layer 15 are kept intimate. Therefore, it isnot necessary for a sealing material to be applied between the fuel gaspassage formation face 20 b and the anode diffusion layer 15.

Therefore, the number of parts can be reduced and the time and labor ofapplying a seal material can be eliminated, and also the contactresistance between the fuel gas passage formation face 20 b and theanode diffusion layer 15 can be suppressed and the output of the fuelcell raised.

And, as a result of the cathode diffusion layer 16 being broughttogether with the oxidant gas passage formation face 30 b, by theoxidant gas passage grooves 37 . . . and the cathode diffusion layer 16the oxidant gas passages 38 . . . are formed.

Here, by including a thermoplastic resin having good flexibility in thesecond separator 30 it is possible to give the oxidant gas passageformation face 30 b elasticity and make the oxidant gas passageformation face 30 b a part having a good sealing characteristic.

Consequently, the mating parts of the oxidant gas passage formation face30 b and the cathode diffusion layer 16 are kept intimate. Therefore, itis not necessary for a sealing material to be applied between theoxidant gas passage formation face 30 b and the cathode diffusion layer16.

Therefore, the number of parts can be reduced and the time and labor ofapplying a seal material can be eliminated, and also the contactresistance between the oxidant gas passage formation face 30 b and thecathode diffusion layer 16 can be suppressed and the output of the fuelcell raised.

Next, an example of molding the first separator 20 by a fuel cellseparator manufacturing method according to the invention will bedescribed, on the basis of FIG. 5 through FIG. 7.

FIG. 5 is a flow chart of a method for manufacturing a fuel cellseparator according to the first embodiment of the invention. In thefigure, STxx denotes step number.

ST10: A mixture is obtained by kneading together a thermoplastic resinand a conductive material.

ST11: A band-shaped sheet is formed by extrusion-molding the kneadedmixture.

ST12: In one side of this band-shaped sheet, that is, the sidecorresponding to the cooling water passage formation face, cooling waterpassage grooves are press-formed, and in the other side of theband-shaped sheet, that is, the side corresponding to the fuel gaspassage formation face, fuel gas passage grooves are press-formed, and aseparator starting material is thereby obtained.

ST13: By cutting the separator starting material to predetermineddimensions, first separators are obtained.

Referring to FIG. 6A through FIG. 8, ST10 to ST13 of this manufacturingmethod will now be explained in detail.

FIG. 6A and FIG. 6B are views illustrating a step of forming a mixtureinto pellets in this manufacturing method. Specifically, FIG. 6A showsST10 and FIG. 6B shows the first half of ST11.

In FIG. 6A, first, a thermoplastic resin 46 selected from ethylene/vinylacetate copolymers, ethylene/ethyl acrylate copolymers andstraight-chain low-density polyethylene is prepared.

Then, a conductive material 45 of at least one type selected from amonggraphite, Ketjen black, and acetylene black carbon particles isprepared.

The prepared thermoplastic resin 46 and conductive material 45 are fedinto a vessel 48 of a kneading machine 47 as shown with arrows. Thethermoplastic resin 46 and the conductive material 45 fed in are kneadedinside the vessel 48 by kneading vanes (or a screw) 49 being rotated asshown with an arrow.

In FIG. 6B, the mixture 50 is fed into a hopper 52 of a firstextrusion-molding machine 51 and the mixture 50 fed in isextrusion-molded by the first extrusion molding machine 51. By theextrusion-molded molding 53 being passed through a water tank 54, themolding 53 is cooled by water 55 in the water tank 54.

The cooled molding 53 is cut to a predetermined length with a cutter 57of a cutting machine 56, and the cut pellets 58 . . . are stocked in astock tray 59.

FIG. 7 is a view illustrating a pressing step in the above manufacturingmethod, and specifically shows the latter half of ST11 to ST13.

The pellets 58 . . . obtained in the previous step are fed into a hopper61 of a second extrusion-molding machine 60 as shown with an arrow, andthe pellets 58 . . . are extrusion-molded by the secondextrusion-molding machine 60. The extrusion-molded moldings 62 arerolled with rollers 63 to form a band-shaped sheet 64.

A pressing machine 65 is provided on the downstream side of the rollers63, and this pressing machine 65 has upper and lower press dies 66, 67above and below the band-shaped sheet 64.

The upper press die 66 has a press face 66 a facing a second side 64 bof the band-shaped sheet 64, and tongues and grooves (not shown) in thispress face 66 a. The tongues and grooves in the press face 66 a are forpress-forming the fuel gas passage grooves 24 . . . (see FIG. 4) in thesecond side 64 b of the band-shaped sheet 64.

The lower press die 67 has a press face 67 a facing a first side 64 a ofthe sheet 64, and has tongues and grooves (not shown) in this press face67 a. These tongues and grooves in the press face 67 a are forpress-forming the cooling water passage grooves 21 . . . (see FIG. 4) inthe first side 64 a of the band-shaped sheet 64.

The upper and lower press dies 66, 67 are disposed at a press startingposition P1, both sides 64 a, 64 b of the band-shaped sheet 64 arepressed with the upper and lower press dies 66, 67, and with this statebeing maintained the upper and lower press dies 66, 67 are moved asshown by the arrows a, b at the extrusion speed of the band-shaped sheet64.

Thus, cooling water passage grooves 21 . . . are press-formed in thefirst side 64 a of the band-shaped sheet 64, i.e. the side correspondingto the cooling water passage formation face 20 a (see FIG. 4), and fuelgas passage grooves 24 . . . are press-formed in the second side 64 b ofthe band-shaped sheet 64, i.e. the side corresponding to the fuel gaspassage formation face 20 b (see FIG. 4), whereby the band-shaped sheet64 is formed into a separator starting material 68.

When the upper and lower press dies 66, 67 reach a press releasingposition P2, the upper and lower press dies 66, 67 move away from theband-shaped sheet 64 as shown by the arrows c and d, and after the upperand lower press dies 66, 67 have reached a predetermined position on therelease-side, the upper and lower press dies 66, 67 move toward theupstream side as shown by the arrows e and f.

When the upper and lower press dies 66, 67 have reached a predeterminedposition on the press start-side, the upper and lower press dies 66, 67are moved to the press start position P1 as shown by the arrows g and h.

By the steps described above being repeated in turn, the cooling waterpassage grooves 21 . . . and fuel gas passage grooves 24 . . . arepress-formed in the sides 64 a, 64 b of the band-shaped sheet 64.

In FIG. 7, to facilitate understanding, an example was illustratedwherein one each of the upper and lower press dies 66, 67 were provided;however, in practice a plurality of each of the upper and lower pressdies 66, 67 are provided.

By a plurality of each of the upper and lower press dies 66, 67 beingprovided, cooling water passage grooves 21 . . . and fuel gas passagegrooves 24 . . . (see FIG. 4) can be press-formed continuously in thesides 64 a, 64 b of the band-shaped sheet 64.

The upper and lower press dies 66, 67 have parts for forming the fuelgas supply opening 26 a and the fuel gas discharge opening 26 b shown inFIG. 1. And, the upper and lower press dies 66, 67 have parts forforming the oxidant gas supply opening 29 a and the oxidant gasdischarge opening 29 b shown in FIG. 1.

Also, the upper and lower press dies 66, 67 have parts for forming thecooling water supply opening 23 a and the cooling water dischargeopening 23 b shown in FIG. 1.

Thus, as well as the cooling water passage grooves 21 . . . and the fuelgas passage grooves 24 . . . being formed in the sides 64 a, 64 b of theband-shaped sheet 64 with the upper and lower press dies 66 and 67, thecooling water supply opening 23 a and the gas supply openings 26 a, 29 aand the cooling water discharge opening 23 b and the gas dischargeopenings 26 b, 29 b shown in FIG. 1 are formed at the same time.

A cutter device 70 is provided above the separator starting material 68obtained in the previous step, on the downstream side of the pressingmachine 65.

By a cutter 71 of this cutter device 70 being lowered as shown by thearrow i, the separator starting material 68 is cut to a predetermineddimension and first separators 20 . . . are obtained. This ends theprocess of manufacturing the first separator 20.

Thus, in this method for manufacturing a fuel cell separator accordingto the invention, the cooling water passage grooves 21 . . . and thefuel gas passage grooves 24 . . . are press-formed in the sides 64 a, 64b of the mixture 50 in the form of a band-shaped sheet 64, and then thesheet 64 is cut to a predetermined dimension to obtain first separators20.

By the cooling water passage grooves 21 . . . and the fuel gas passagegrooves 24 . . . being press-formed in the sheet 64 state, the coolingwater passage grooves 21 . . . and the fuel gas passage grooves 24 . . .can be molded continuously with good efficiency and the productivity ofthe first separator 20 can be raised.

Although an example of forming the first separator 20 has been describedin connection with FIG. 5 through FIG. 7, the second separator 30 canalso be manufactured by the same method as the manufacturing method ofthe first separator 20.

However, the second separator 30 does not have the cooling water passagegrooves 21 . . . (see FIG. 4) like the first separator 20, and has aflat bonding face 30 a. Because of this, the lower press die 67 shown inFIG. 7 does not need to have tongues and grooves for press-formingcooling water passage grooves 21 . . . in the first side of theband-shaped sheet 64 in its face facing the first side of theband-shaped sheet 64.

A variation of the first embodiment will now be described.

Whereas in the first embodiment an example was described wherein theproportion of the thermoplastic resin included in the first and secondseparators 20, 30 was made 14 to 20 wt % and the proportion of thecarbon particles was made 80 to 86 wt %, as a variation of the firstembodiment the proportion of the thermoplastic resin included in thefirst and second separators 20, 30 can be made 14 to 20 wt %, theproportion of the carbon particles made 70 to 83.5 wt % and a proportionof glass fibers or carbon fibers made 2.5 to 10 wt %.

By glass fibers or carbon fibers being mixed with the mixture, the firstand second separators 20, 30 of this variation of the first embodimentcan be made more rigid.

Here, the reasons for setting the glass fiber or carbon fiber content to2.5 to 10 wt % are as follows.

When the glass fiber or carbon fiber content is less than 2.5 wt %, theglass fiber or carbon fiber content is too small and it is difficult toraise the rigidity of the first and second separators 20, 30.

On the other hand, when the glass fiber or carbon fiber content exceeds10 wt %, the glass fiber or carbon fiber content is too large and it isdifficult to disperse the glass fibers or carbon fibers uniformly in themixture and the extrusion-molding and press-forming of the mixturebecome problematic.

Accordingly, the glass fiber or carbon fiber content is set to 2.5 to 10wt %, whereby the rigidity of the first and second separators 20, 30 israised and a mixture having good moldability is obtained.

The reasons for making the carbon particle content 70 to 83.5 wt % inthis variation of the first embodiment are as follows.

When the carbon particle content is less than 70 wt %, the carbonparticle content is too small and it is difficult to reduce the volumeresistivity (Ω·cm) of the first and second separators 20, 30, and it isdifficult to secure an adequate electrical conductivity of the first andsecond separators 20, 30.

On the other hand, as mentioned above, when the carbon particle contentexceeds 86 wt %, the carbon particle content is too large and it isdifficult to disperse the carbon particles uniformly, andextrusion-molding and press-forming become problematic. Therefore, it isdesirable that the carbon particle content be set to 86 wt % or below.

However, because 14 to 20 wt % of the thermoplastic resin and 2.5 to 10wt % of glass fibers or carbon fibers are included in the first andsecond separators 20, 30, in this variation, the carbon particle contentis made 83.5 wt % or below, whereby the carbon particles can bedispersed uniformly and extrusion-molding and press-forming can becarried out well.

When the carbon particle content is set to 70 to 83.5 wt % like this,the volume resistivity (Ω·cm) is reduced and a mixture having goodmoldability is obtained.

With the first and second separators 20, 30 of this variation of thefirst embodiment, the same effects as those of the first embodiment canbe obtained, and in addition, as a result of the glass fibers or carbonfibers being mixed in, the rigidity of the first and second separators20, 30 is raised.

Next, a second embodiment will be described, on the basis of FIG. 8through FIG. 14. Parts in this second embodiment the same as parts inthe first embodiment have been given the same reference numerals andwill not be described again.

First, reference will be made to FIG. 1, which is an explodedperspective view of a fuel cell with a fuel cell separator according tothe second embodiment of the invention.

Only the separator 118 (a first separator 120 and a second separator130) of the fuel cell 110 of this second embodiment differs from thefuel cell 10 of the first embodiment, and the rest of its constructionis the same as the fuel cell 10 of the first embodiment.

The separator 118 (first separator 120 and second separator 130) will bedescribed below.

The first and second separators 120, 130 are made from a mixtureincluding 10 to 34 wt % of polyphenylene sulfide, 60 to 80 wt % ofgraphite, 1 to 10 wt % of Ketjen black, and 5 to 15 wt % of choppedcarbon fiber.

10 to 34 wt % of polyphenylene sulfide is included in the first andsecond separators 120, 130 as a thermoplastic resin. Becausepolyphenylene sulfide is a resin having superior moldability andsuperior elasticity, the moldability of when the first and secondseparators 120, 130 are injection-molded is raised and first and secondseparators 120, 130 having an excellent sealing characteristic areobtained.

By this means, the productivity and accuracy of the first and secondseparators 120, 130 are raised further.

Moreover, because polyphenylene sulfide is a resin having excellentheat-resistance, by polyphenylene sulfide being included in the firstand second separators 120, 130, the heat-resistance of the first andsecond separators 120, 130 is raised.

Consequently, application to fuel cells used at relatively hightemperatures becomes possible, and the range of uses can be enlarged.

The reasons for setting the polyphenylene sulfide content to 10 to 34 wt% are as follows.

When the polyphenylene sulfide content is less than 10 wt %, thepolyphenylene sulfide content is too low and it becomes difficult tosecure moldability of the first and second separators 120, 130 andelasticity of the contact faces of the first and second separators 120,130, i.e. sealing characteristic.

Also, when the included amount is less than 10 wt %, it is difficult tosecure heat-resistance of the first and second separators 120, 130 andto make it work as a bonding agent.

When on the other hand the polyphenylene sulfide content exceeds 34 wt%, the graphite content in the first and second separators 120, 130 istoo small and it is difficult to secure adequate electrical conductivityof the first and second separators 120, 130.

Accordingly, the thermoplastic resin content was set to 10 to 34 wt %,whereby moldability, sealing characteristic, heat-resistance and bondingcharacteristic of the first and second separators 120, 130 are securedand a sufficient electrical conductivity is secured.

Also, by 60 to 80 wt % of graphite being included in the first andsecond separators 120, 130, their electrical conductivity was raised.

The reasons for setting the graphite content to 60 to 80 wt % are asfollows.

When the graphite content is less than 60 wt %, the graphite content istoo small and it is difficult to raise the electrical conductivity ofthe first and second separators 120, 130.

On the other hand, when the graphite content exceeds 80 wt %, thegraphite content is too large and it is difficult to disperse thegraphite uniformly, and extrusion-molding and press-forming becomeproblematic.

Accordingly, the graphite content is set to 60 to 80 wt %, wherebyelectrical conductivity of the first and second separators 120, 130 issecured and moldability is secured.

By the graphite content being made at least 60 wt %, the volumeresistivity (mΩ·cm) is reduced and the electrical conductivity of thefirst and second separators 120, 130 is amply raised.

Also, by 1 to 10 wt % of Ketjen black being included in the first andsecond separators 120, 130, the electrical conductivity is raised stillfurther.

Ketjen black is a material with particularly good electricalconductivity compared to other carbon blacks, and by Ketjen black beingincluded in the first and second separators 120, 130 the electricalconductivity of the first and second separators 120, 130 is raised more.

Here the reasons for setting the Ketjen black content to 1 to 10 wt %are as follows.

If the Ketjen black content is less than 1 wt %, there is a risk of notbeing possible to secure electrical conductivity of the first and secondseparators 120, 130 adequately because the Ketjen black content is toosmall.

If on the other hand the Ketjen black content exceeds 10 wt %, kneadingbecomes difficult because the Ketjen black content is too large.Although it is conceivable to make kneading possible by adding asolvent, there is a risk of costs increasing as a result of using asolvent.

Furthermore, even if a solvent is added and kneading is completedsuccessfully, the fluidity of the knead including the Ketjen black isrelatively poor and for example at the time of molding it is difficultto obtain the predetermined shape.

Accordingly, the Ketjen black content was set to 1 to 10 wt % to secureadequate electrical conductivity of the first and second separators 120,130 and also achieve facilitation of kneading and secure goodmoldability.

The graphite and Ketjen black included in the first and secondseparators 120, 130 are carbon particles, and no large quantity offibrous material is included in the separators. Therefore, theoccurrence of directionality in the separators caused by fibrousmaterial is suppressed, and warping and distortion arising in the firstand second separators 120, 130 as a result of anisotropy is prevented.

Also, because no large quantity of fibrous material is included in thefirst and second separators 120, 130, the strength of the first andsecond separators 120, 130 is prevented from falling due to weld linesarising in the gas passage grooves and the cooling water passage groovesprovided on the first and second separators 120, 130.

Also, by 5 to 15 wt % of chopped carbon fiber being included in thefirst and second separators 120, 130, the strength and theheat-resistance of the first and second separators 120, 130 are raised.

Here, the reasons for setting the chopped carbon fiber content 5 to 15wt % are as follows.

When the chopped carbon fiber content is less than 5 wt %, the choppedcarbon fiber content is too small, and it is difficult to securestrength and heat-resistance of the first and second separators 120,130.

On the other hand, when the chopped carbon fiber content exceeds 15 wt%, the amount of the chopped carbon fiber included in the first andsecond separators 120, 130 is too large and the directionality of thechopped carbon fiber manifests conspicuously and the first and secondseparators 120, 130 become anisotropic. Consequently, there is a risk ofwarping and distortion arising in the first and second separators 120,130.

And, when as in the first and second separators 120, 130 there are gaspassage grooves and cooling water passage grooves in the side faces,weld lines tend to appear. Consequently, there is a risk of the strengthof the first and second separators 120, 130 falling drastically.

Accordingly, the chopped carbon fiber content was set to 5 to 15 wt %,whereby strength and durability of the first and second separators 120,130 were secured.

Here, the viscosity of the polyphenylene sulfide included in the firstand second separators 120, 130 is set to 20 to 80 psi.

The reasons for setting the viscosity of the polyphenylene sulfide to 20to 80 psi are as follows.

When the viscosity of the polyphenylene sulfide is less than 20 psi, theviscosity is too low and in the manufacturing of the first and secondseparators 120, 130 the polyphenylene sulfide does not harden and formsa slurry.

On the other hand, when the viscosity of the polyphenylene sulfideexceeds 80 psi, the viscosity of the polyphenylene sulfide is too highand in the manufacturing of the first and second separators 120, 130 thegraphite and so on cannot be kneaded well into the polyphenylenesulfide.

Accordingly, the viscosity of the polyphenylene sulfide is set to 20 to80 psi, whereby it is made possible to knead the graphite and so on intothe polyphenylene sulfide well and the moldability of the separator israised further.

The viscosity of the polyphenylene sulfide is that measured by the MFR(Melt Flow Rate) test method at 300° C. (ASTM D1238).

MFR is a method wherein a vertical metal cylinder is filled withpolyphenylene sulfide, this polyphenylene sulfide is pressed with apiston loaded with a weight and extruded through a die at the end of thecylinder, and the movement time taken for the piston to move apredetermined distance at this time is measured and the viscosityobtained on the basis of this measured value.

Next, referring to FIG. 9, the first separator 120 is a member formed ina substantially rectangular shape (see FIG. 8), and has many coolingwater passage grooves 21 . . . in a cooling water passage formation face20 a and has many fuel gas passage grooves 24 . . . in a fuel gaspassage formation face 20 b.

10 to 34 wt % of polyphenylene sulfide is included in the firstseparator 120. By this means, moldability, sealing characteristic,heat-resistance and bonding characteristic of the first separator 120are secured, and an ample electrical conductivity is secured.

Because the elastic modulus of the chopped carbon fiber included in thefirst separator 120 is high, when the chopped carbon fiber content istoo large, chopped carbon fiber cannot get into the ribs 140 . . .forming the cooling water passage grooves 21 . . . or into the ribs 141. . . forming the fuel gas passage grooves 24 . . . , and separation ofthe chopped carbon fiber and the polyphenylene sulfide tends to occur.

Consequently, there is a risk of the ribs 140 . . . , 141 . . . having ahigher polyphenylene sulfide content compared to other parts, and notbeing able to exhibit their proper performance.

Accordingly, the chopped carbon fiber content was made 5 to 15 wt %. Inthis way, the chopped carbon fiber is made to enter into the ribs 140 .. . , 141 . . . well and the ribs 140 . . . , 141 . . . are formed well.

As shown in FIG. 10, the second separator 130 is a member formed in asubstantially rectangular shape as shown in FIG. 8, and has a bondingface 30 a formed flat and has many oxidant gas passage grooves 37 . . .in an oxidant gas passage formation face (contact face) 30 b.

10 to 34 wt % of polyphenylene sulfide is included in the secondseparator 130. By this means, moldability, sealing characteristic,heat-resistance and bonding characteristic of the second separator 130are secured, and an ample electrical conductivity is secured.

Like the first separator 120, in the second separator 130 also, becausethe chopped carbon fiber content is kept to 5 to 15 wt %, the choppedcarbon fiber is made to enter into the ribs 142 . . . well and the ribs142 . . . are formed well.

Next, reference will be made to FIG. 11, which shows the electrodediffusion layers 15, 16 stacked with the separator 118.

The separator 118 is made by bonding together the cooling water passageformation face 20 a of the first separator 120 and the bonding face 30 aof the second separator 130 and covering the cooling water passagegrooves 21 in the first separator 120 with the second separator 130 toform cooling water passages 22.

By the anode diffusion layer 15 being set against the fuel gas passageformation face 20 b, fuel gas passages 25 . . . are formed by the fuelgas passage grooves 24 . . . and the anode diffusion layer 15.

Because 5 to 15 wt % of chopped carbon fiber is included in thisseparator 118, its strength, elastic modulus and heat-resistance areraised further. By the strength of the separator 118 being raised, thetightening strength of when the separator 118 is assembled to the fuelcell is raised.

Also, by the elastic modulus and the heat-resistance of the separator118 being raised, resistance to gas pressure and creep strength at hightemperatures are raised, and it becomes possible for the fuel cell to beused suitably even at high temperatures.

Next, in FIG. 12, it will be explained how the volume resistivity ρv isobtained. First, an example of obtaining the volume resistivity ρv of asample 150 (width W, height t, length L) by the four probe method (ASTMD991) will be described.

A fixed current I is passed as shown with an arrow from a first end 151of cross-sectional area (W×t) to a second end 152, and the potentialdifference V between an electrode on the first end 151 side and anelectrode on the second end 152 side, which are separated by thedistance L, is measured by the four probe method.

On the basis of the measured potential difference V, the volumeresistivity ρv is obtained using the following equation.Volume Resistivity ρv=(V/I)×(W/L)×t

The reasons for employing the four probe method will be explained.

In the measurement of the potential difference V, when the fixed currentI is passed through the sample 150, a voltage drop called contactresistance occurs as a result of an interface phenomenon between thefirst end 151 of the sample 150 and the current electrode. Due to theinfluence of this contact resistance, the resistance Ω (V/I) measureshigh.

To avoid this, by using the four probe method, contact resistance iseliminated and the true volume resistivity ρv of the sample 150 isobtained.

As the method of measuring the potential difference V, besides the fourprobe method, the double ring method (ASTM D257) is also known.

However, the double ring method is suited to the measurement of highresistances, and even in measurement results obtained by the presentinventors it was found that compared with the four probe method thevolume resistivity measures considerably low.

Volume resistivities obtained by the four probe method (ASTM D991) andthe double ring method (ASTM D257) will be discussed below on the basisof Test Examples 1 and 2 of Table 1. TABLE 1 Density Test Example 1 TestExample 2 Blend polyphenylene viscosity 60 psi 1.35 15 wt % 12.5 wt %composition sulfide viscosity 20 psi 1.35 15 wt % 12.5 wt % plasticizer(polymer type) 0.95 — 2.5 wt % graphite 2.3 69 wt % 69 wt % Ketjen black1.8 1 wt % 1 wt % chopped carbon fiber (PAN) 1.75 — 2.5 wt % fluidity ofblend composition 30 45 (spiral flow ratio) Volume four probe method(ASTM D991) 0.57 mΩ/cm 0.33 mΩ/cm Resistivity double ring method (ASTMD257) 0.155 mΩ/cm 0.072 mΩ/cm

As shown in Table 1, the test piece of Test Example 1 included 15 wt %polyphenylene sulfide (viscosity 60 psi), 15 wt % polyphenylene sulfide(viscosity 20 psi), 69 wt % graphite (particle diameter 100 μm), and 1wt % Ketjen black.

The viscosity of this mixture is spiral flow ratio 30.

The test piece of Test Example 2 included 12.5 wt % polyphenylenesulfide (viscosity 60 psi), 12.5 wt % polyphenylene sulfide (viscosity20 psi), 2.5 wt % plasticizer (polymer type), 69 wt % graphite (particlediameter 100 μm), 1 wt % Ketjen black and 2.5 wt % PAN chopped carbonfiber.

The viscosity of this mixture is spiral flow ratio 45.

A spiral flow ratio is a ratio obtained in a spiral flow test. A spiralflow test is a test wherein molten resin is injected by means of aninjection-molding machine into a narrow and long spiral-shaped grooveformed in a die and its moldability is determined from the flow lengthof the molten resin flowing into the spiral-shaped groove.

The volume resistivities of the test piece of Test Example 1 and thetest piece of Test Example 2 were obtained by the four probe method andby the double ring method.

The volume resistivities obtained by the double ring method were TestExample 1: 0.155 mΩ·cm and Test Example 2: 0.072 mΩ·cm.

The volume resistivities obtained by the four probe method, on the otherhand, where Test Example 1: 0.57 mΩ·cm and Test Example 2: 0.33 mΩ·cm.

Thus was found that when a volume resistivity in a low resistance rangeis measured by the double ring method, which is suited to highresistance ranges, the volume resistivity becomes considerably lowcompared to the four probe method. So, to raise reliability, it wasdecided that volume resistivities would be measured by the four probemethod.

Next, relationships between volume resistivity and graphite and Ketjenblack contents obtained by the four probe method will be discussed, withreference to FIGS. 13 and 14.

In the graph of FIG. 13, the vertical axis shows volume resistivity(mΩ·cm) and the horizontal axis shows graphite content (wt %).

It can be seen that when the graphite content is 0, the volumeresistivity is about 150000 mΩ·cm, but when the graphite content is 60wt % or more, the volume resistivity is low.

Therefore, the graphite content was set to at least 60 wt %, andpreferably at least 65 wt %.

In the graph of FIG. 14, the vertical axis shows volume resistivity(mΩ·cm) and the horizontal axis shows Ketjen black content (wt %).

When the Ketjen black content is 0, the volume resistivity is about 3400mΩ·cm, but when the Ketjen black content reaches 1 wt % the volumeresistivity is down to about 500 mΩ·cm.

Also, it can be seen that when the Ketjen black content is 2, the volumeresistivity is about 300 mΩ·cm, and when the Ketjen black contentreaches 3 wt % the volume resistivity is extremely small.

Therefore, the Ketjen black content was set to be at least 1 wt %.

Next, Test Examples 1 to 3 and Comparison Examples 1 and 2 will bediscussed on the basis of Table 2.

For the polyphenylene sulfide included in the separator 118, as anexample that manufactured by Idemitsu Petrochemical Co., Ltd. was used,and for the graphite as an example that manufactured by Nippon GraphiteIndustries, Ltd. was used.

For the Ketjen black, as an example EC600JD (trade name) made by KetjenBlack International Co., Ltd (sold by Mitsubishi Chemical Co., Ltd.) wasused, and for the chopped carbon fiber, as an example a PAN type made byToray Industries, Inc. was used.

EC600JD (trade name) made by Ketjen Black International Co., Ltd is ahigh-grade, highly conductive carbon black that provides the sameelectrical conductivity as an ordinary Ketjen black with only about 60%of the content.

The chopped carbon fiber made by Toray Industries, Inc. is a carbonfiber of diameter d 7 μm and length 3 mm. TABLE 2 Comparison Ex.Comparison Ex. Test Ex. 1 Test Ex. 2 Test Ex. 3 1 2 Blend polyphenylene33.25 wt % 30 wt % 25 wt % 35 wt % 35 wt % composition sulfide(viscosity 45 psi) (viscosity 45 psi) (viscosity 45 psi) (viscosity 80psi) (viscosity 80 psi) graphite 60 wt % 63 wt % 67 wt % 58 wt % 62 wt %(particle 100 μm) (particle 100 μm) (particle 100 μm) (particle 100 μm)(particle 100 μm) Ketjen black 2.85 wt % 2 wt % 3 wt % 2 wt % 3 wt %(EC600JD) (EC600JD) (EC600JD) (EC600JD) (EC600JD) chopped carbon 5 wt %5 wt % 5 wt % 5 wt % — fiber (PAN) (PAN) (PAN) (PAN) fluidity of blendcomposition 40 45 60 62 50 (spiral flow ratio) volume resistivity 72mΩ.cm 85 mΩ.cm 60 mΩ.cm 330 mΩ.cm 98 mΩ.cm verdict ◯ ◯ ◯ X Xpolyphenylene sulfide: Idemitsu Petrochemical Co., Ltd.graphite: Nippon Graphite Industries, Ltd.Ketjen black: Ketjen Black International Co., Ltd.chopped carbon fiber: Toray Industries, Inc.

As shown in Table 2, Test Example 1 includes 33.25 wt % of polyphenylenesulfide (viscosity 45 psi), 60 wt % of graphite (particle diameter 100μm), 2.85 wt % of Ketjen black, and 5 wt % of chopped carbon fiber. Theviscosity of this mixture is spiral flow ratio 40.

Test Example 2 includes 30 wt % of polyphenylene sulfide (viscosity 45psi), 63 wt % of graphite (particle diameter 100 μm), 2 wt % of Ketjenblack, and 5 wt % of chopped carbon fiber. The viscosity of this mixtureis spiral flow ratio 45.

Test Example 3 includes 25 wt % of polyphenylene sulfide (viscosity 45psi), 67 wt % of graphite (particle diameter 100 μm), 3 wt % of Ketjenblack, and 5 wt % of chopped carbon fiber. The viscosity of this mixtureis spiral flow ratio 60.

Comparison Example 1 includes 35 wt % of polyphenylene sulfide(viscosity 80 psi), 58 wt % of graphite (particle diameter 100 μm), 2 wt% of Ketjen black, and 5 wt % of chopped carbon fiber. The viscosity ofthis mixture is spiral flow ratio 62.

Comparison Example 2 includes 35 wt % of polyphenylene sulfide(viscosity 80 psi), 62 wt % of graphite (particle diameter 100 μm), and3 wt % of Ketjen black. The viscosity of this mixture is spiral flowratio 50.

Samples of Test Examples 1 to 3 and Comparison Examples 1 and 2 wereprepared, and then the volume resistivities of the samples were obtainedby the four probe method explained with reference to FIG. 12.

Here, from the expectation that if the volume resistivity is 90 mΩ·cm orless the mixture will provide a sufficient electrical conductivity whenused in the separator 18 (see FIG. 1), a volume resistivity thresholdvalue was made 90 mΩ·cm, and when the volume resistivity obtained was 90mΩ·cm or lower an evaluation of OK was made and when the volumeresistivity obtained was above 90 mΩ·cm an evaluation of X was made.

The results were that Test Example 1 had its volume resistivity kept to72 mΩ·cm, which is below 90 mΩ·cm and therefore the evaluation was OK.

Test Example 2 had its volume resistivity kept to 85 mΩ·cm, which isbelow 90mΩ·cm and therefore the evaluation was OK.

And Test Example 3 had its volume resistivity kept to 60 mΩ·cm, which isbelow 90 mΩ·cm and therefore the evaluation was OK.

On the other hand, Comparison Example 1 had a volume resistivity of 330mΩ·cm, which is over 90 mΩ·cm and so the evaluation was X.

And Comparison Example 2 had a volume resistivity of 98 mΩ·cm, which isover 90 mΩ·cm and so the evaluation was X.

As for the fluidity of the mixture, considering moldability and so on,it must be at least 30 by spiral flow ratio, and preferably should be atleast 40.

In the cases of Test Example 1 to Test Example 3 and Comparison Example1 and Comparison Example 2, because the fluidities of the mixtures wereall above 40 by spiral flow ratio, for example injection-molding waspossible.

Next, a variation of the second embodiment will be described.

Although in the second embodiment an example was described wherein 10 to34 wt % of polyphenylene sulfide, 60 to 80 wt % of graphite, 1 to 10 wt% of Ketjen black and 5 to 15 wt % of chopped carbon fiber were includedin the first and second separators 120, 130, as a variation of thesecond embodiment it is possible to include 10 to 34 wt % ofpolyphenylene sulfide, 65 to 80 wt % of graphite, and 1 to 10 wt % ofKetjen black in the first and second separators 120, 130.

With this variation of the second embodiment, by 10 to 34 wt %polyphenylene sulfide being included in the first and second separators120, 130, the moldability of the first and second separators 120, 130when they are injection-molded is raised, and first and secondseparators 120, 130 having an excellent sealing characteristic areobtained.

As a result, the productivity and the accuracy of the first and secondseparators 120, 130 are raised further.

Also, because polyphenylene sulfide is a resin having goodheat-resistance, by polyphenylene sulfide being included in the firstand second separators 120, 130′, the heat-resistance of the first andsecond separators 120, 130 is raised. Consequently, application to fuelcells used at relatively high temperatures becomes possible, and therange of uses can be enlarged.

The reasons for setting the polyphenylene sulfide content to 10 to 34 wt% in this variation of the second embodiment are the same as in thesecond embodiment.

By 65 to 80 wt % of graphite being included in the first and secondseparators 120, 130, the electrical conductivity is raised.

The reasons for setting the graphite content to 65 to 80 wt % are thesame as in the second embodiment.

That is, when the graphite content is less than 65 wt %, it is difficultto raise the electrical conductivity of the first and second separators120, 130 because the graphite content is too small.

When on the other hand the graphite content exceeds 80 wt %, thegraphite content is too large and it becomes difficult to disperse thegraphite uniformly, and the extrusion-molding and press-forming becomeproblematic.

Accordingly, the thermoplastic resin content was set to 65 to 80 wt %,whereby electrical conductivity of the first and second separators 120,130 is secured and moldability is secured.

By making the graphite content over 65 wt %, it is possible to reducethe volume resistivity (mΩ·cm) of the first and second separators 120,130 and raise the electrical conductivity of the first and secondseparators 120, 130 amply.

Furthermore, by including 1 to 10 wt % of Ketjen black in theseparators, it is possible to raise the electrical conductivity stillfurther.

The reasons for setting the Ketjen black content to 1 to 10 wt % in thevariation of the second embodiment are the same as in the secondembodiment.

With the first and second separators 120, 130 of this variation of thesecond embodiment, the same effects as those of the second embodimentcan be obtained.

Although in the foregoing first and second embodiments solid polymerfuel cells 10, 110 in which solid polymer electrolyte films were used asthe electrolyte film 12 were described, the invention is not limited tothis, and can also be applied to other fuel cells.

Although in the foregoing first and second embodiments examples weredescribed wherein the first separators 20, 120 and the second separators30, 130 were molded continuously by extrusion-molding and press-forming,the invention is not limited to this, and they can alternatively bemolded by some other manufacturing method such as thermal pressing,injection-molding or transfer molding.

Transfer molding is a method of molding by putting one shot of a moldingmaterial into a pot part other than the cavity and then transferring themolten material into the cavity with a plunger.

Also, whereas in the foregoing first and second embodiments exampleswere described wherein as an example the Ketjen black ‘EC600JD’ made byKetjen Black International Co., Ltd. (sold by Mitsubishi Chemical Co.,Ltd.) was used, there is no limitation to this, and for example ‘EC’made by Ketjen Black International Co., Ltd. can alternatively be used,or some other Ketjen black can be used.

Another carbon black having excellent electrical conductivity likeKetjen black can be used instead of Ketjen black.

Also, although in the second embodiment an example was described whereinthe viscosity of the polyphenylene sulfide included in the first andsecond separators 120, 130 was set to 20 to 80 psi, when the viscosityof the polyphenylene sulfide is higher than 80 psi, this can be dealtwith by the use of a plasticizer.

Also, although in the foregoing second embodiment an example wasdescribed wherein graphite of particle diameter 100 μm was used, theparticle diameter of the graphite is not limited to 100 μm, and someother particle diameter can alternatively be used.

Whereas in the foregoing second embodiment an example was describedwherein a PAN chopped carbon fiber was used, there is no limitation tothis, and alternatively for example a pitch chopped carbon fiber can beused.

INDUSTRIAL APPLICABILITY

As described above, with the present invention it is possible to raisethe productivity of a separators by making their contact faces partswith an excellent sealing characteristic; consequently, the invention isparticularly useful in the field of automobile fuel cells, where therealization of mass production is awaited.

1. A fuel cell separator sandwiching from both sides via diffusionlayers an anode and a cathode set against an electrolyte film, theseparator being made of a mixture of a thermoplastic resin selected fromamong ethylene/vinyl acetate copolymers and ethylene/ethyl acrylatecopolymers and at least one type of carbon particles selected from amongKetjen black, graphite and acetylene black, wherein a proportion of thethermoplastic resin in the mixture is between about 14 to 20 wt %,proportion of the carbon particles is between about 80 to 86 wt %, and 3to 20 wt % of the carbon particles is Ketjen black.
 2. (canceled) 3.(canceled)
 4. A fuel cell separator sandwiching from both sides viadiffusion layers an anode and a cathode set against an electrolyte film,the separator being made of a mixture of a thermoplastic resin selectedfrom among ethylene/vinyl acetate copolymers and ethylene/ethyl acrylatecopolymers, at least one type of carbon particles selected from amongKetjen black, graphite and acetylene black, and glass fiber or carbonfiber, wherein a proportion of the thermoplastic resin in the mixture isbetween about 14 to 20 wt %, a proportion of the carbon particles isbetween 70 to 83.5 wt %, and a proportion of the glass or carbon fiberis between about 2.5 to 10 wt %.
 5. A method for manufacturing a fuelcell separator, comprising the steps of: obtaining a mixture by mixing athermoplastic resin selected from among ethylene/vinyl acetatecopolymers and ethylene/ethyl acrylate copolymers and at least one typeof carbon particles selected from Ketjen black, graphite and acetyleneblack, or by mixing the thermoplastic resin, the carbon particles andglass fiber or carbon fiber; obtaining a sheet material byextrusion-molding the mixture with an extruder; forming gas flow passagegrooves in a surface of the sheet material by moving press dies at theextrusion speed of the sheet material; and obtaining the fuel cellseparator by cutting the sheet material with the gas flow passagesformed therein into a predetermined shape.
 6. A method for manufacturinga fuel cell separator sandwiching from both sides via diffusion layersan anode and a cathode set against an electrolyte film, the methodcomprising the steps of: providing polyphenylene sulfide having Haviscosity of 20 to 80 psi, graphite and Ketjen black; obtaining amixture by mixing 10 to 34 wt % polyphenylene sulfide, 65 to 80 wt %graphite and 1 to 10 wt % Ketjen black; and, molding the mixture toprovide the fuel cell separator.
 7. The method for manufacturing a fuelcell separator according to claim 6, wherein the mixture furtherincludes between about 5 to 15 wt % chopped carbon fiber and thegraphite included in the mixture is between about 60 to 80 wt %. 8.(canceled)
 9. The method for manufacturing a fuel cell separatoraccording to claim 5, wherein the mixture includes between about 14 to20 wt % of the thermoplastic resin and between about 80 to 86 wt % ofthe carbon particles and between about 3 to 20 wt % of the carbonparticles is Ketjen black.
 10. The method for manufacturing a fuel cellseparator according to claim 5, wherein the mixture includes betweenabout 14 to 20 wt % of the thermoplastic resin, between about 70 to 83.5wt % of the carbon particles, and between about 2.5 to 10 wt % of theglass or carbon fiber.